A. Field of the Invention
The present invention relates generally to two-way communication and control systems, and, more particularly, to communication and control systems in which a number of remotely positioned controllable devices such as circuit breakers, motor control relays, lighting systems, and the like may be controlled from a central or master controller over a common network line.
While the invention is of general application in such control systems, it is particularly suitable for use with and will be described in connection with a line carrier control subsystem intended for residential use in conjunction with a load management terminal associated with the watt hour meter of the residence and controlled by a public utility over its power distribution system. Specifically, the present invention is concerned with a low cost software based digital IC which is pin configurably to operate either as a central controller associated with the utility load management terminal, or as a slave unit associated with a particular circuit breaker controlling a predetermined residential load device, or as a customer service unit by means of which the residential utility customer can be informed of the existing utility rate schedule, i.e. the cost of AC power per kw hour, and can control certain slave units associated with different residential loads by selectively activating corresponding switches on the customer service unit.
B. Description of the Prior Art
Various communication and control systems have been heretofore proposed for controlling a group of remotely located devices from a central controller over a common network line, such as a power line. For example, in Feiker U.S. Pat. Nos. 4,173,754 and 4,185,272 an arrangement is disclosed wherein a redundant digital address and function code is generated at a control station which is transmitted over a power line to a group of receiver-decoders individually associated with different controlled apparatus. However, the central station requires a relatively complex and expensive CPU, such as an Intel 8080A, and one or more separate random access memories. Also, the receiver-decoder at each remote station is of the type shown in Eichelberger et al U.S. Pat. No. 4,091,361 wherein a large number of hardware components are employed to receive and decode a message and exercise a desired control function. With such an arrangement it is not possible to provide a common software based digital IC which can function as either a central controller or a remote receiver-decoder by simply selecting different pins on the digital IC to establish the desired function of the device. Furthermore, in the prior art arrangement of these patents noise immunity is said to be achieved by redundantly transmitting the digital address and function code and delaying performance of the desired control function until the correct address portion of the code has been received at least two times out of three. However, such an arrangement substantially reduces the throughput of the system because it requires transmitting each message a minimum of three times irrespective of the noise level on the common network line.
Eichelberger et al U.S. Pat. No. 4,213,182 and Miller U.S. Pat. No. 4,167,786 also disclose a communication and control system in which the central controller requires a relatively complex and expensive CPU and the load control processor at each remote station is hardware based. Also, the system disclosed in these patents requires the transmission of complementary bytes for both address and data to provide security against errors in transmission. In Miller, et al U.S. Pat. No. 4,367,414 a further type of communication and control system is disclosed in which different types of microcomputers are employed at the central station and at a large number of remote stations which are connected to the central stastion by means of a dedicated twisted pair line as the common network line. U.S. Pat. Nos. 4,213,182, 4,167,786 and 4,367,414 are not concerned with the transmission of modulated carrier signals over a power line or the reception of such signals in the noisy environment usually encountered on power lines.
There have also been developed various types of communication systems for electrical distribution networks wherein a power line carrier system is employed to provide communication between the central station and load management terminals which are utilized as end devices in the utility's distribution network communication system. Such communication systems and load management terminals are shown in Whyte U.S. Pat. No. 3,911,415, Whyte U.S. Pat. No. 3,942,168, York U.S. Pat. No. 4,427,968, Kennon et al. U.S. Pat. No. 4,402,059 and Kennon U.S. Pat. No. 4,429,366.